The present invention relates generally to the recovery of corn germ and optionally corn coarse fiber (pericarp) from corn, and more particularly to processes for the recovery of corn germ and optionally corn coarse fiber by flotation (e.g., through the use of enzymes such as amylases, proteases, cell wall degrading enzymes, or mixtures thereof).
Corn coarse fiber (also known as pericarp or pericarp fiber or bran) is the outer covering of a kernel of corn, and is a product that can be used as feedstock for the production of such end products as Corn Fiber Gum (CFG) and Corn Fiber Oil. Corn Fiber Gum can be used in both food and non-food applications as a film former, an emulsifier, a low-viscosity bulking agent, an adhesive, or as a substitute for gum Arabic. Corn Fiber Oil has three natural phytosterol compounds (ferulate phytosterol esters or “FPE,” free phytosterols or “St,” and phytosterol fatty acyl esters or “St:E”) that have been found to lower serum cholesterol in blood, and therefore can be used as a nutraceutical product. Such products command high dollar values in the market (approximately $8.00 to $9.00 per pound).
One of the many end-products in which corn is used as the base-product is ethanol. Currently, ethanol is being produced from corn mainly via two different processes: a wet mill process and a dry-grind process (which is not to be confused with a dry-milling process).
In wet milling, corn is separated into its different components (germ, fiber, protein, and starch) using various separation techniques. The clean starch is then cooked, saccharified, fermented, and distilled to make ethanol. Wet milling is a very capital intensive process, but these costs are offset by the resulting high value co-products of the process (such as corn oil produced from the germ, gluten meal from the protein, and gluten feed from the fiber and solubles).
In the other primary process for producing ethanol, the dry-grind process, raw corn is ground, mixed with water, cooked, saccharified, fermented, and then distilled to make ethanol. However, while the only fermentable product in corn is the starch, the other non-fermentable components of the corn (e.g., the germ, the fiber, and the protein) are carried through the remainder of the dry-grind processing steps, and are recovered at the end as distillers dried grains with solubles (DDGS). In current dry-grind processes, neither the germ nor the pericarp are recovered separately, but instead these components end up as part of the DDGS.
The dry-grind process is not a very capital intensive process (when compared with the wet-mill process), but the primary co-product produced (DDGS, which is a livestock feed product) is a relatively low value product. Accordingly, because of the low value co-product, the net corn cost is higher in dry-grind ethanol plants that it is in wet-mill plants. Thus, when corn prices increase, it is very difficult to economically justify operating dry-grind ethanol plants that can only produce low value co-products with the ethanol.
One strategy for reducing the net corn cost in dry-grind ethanol plants is to recover co-products other than DDGS, especially non-fermentable co-products. Previously, modifications to conventional dry-grind ethanol plants that enabled the recovery of the germ were studied. This modified dry grind ethanol process is known as the “Quick Germ” process described in U.S. Pat. No. 6,254,914, and involves soaking whole kernel corn in water before degermination. The germ is then recovered by flotation (which involves the addition of corn starch, thin stillage, a salt such as sodium nitrate, and/or sugar syrup such as high fructose corn syrup or dextrose) and the use of germ hydrocyclones, and the remainder of the corn is ground and processed for ethanol production. Economic analysis has shown that the “Quick germ” process has the potential to reduce the cost of ethanol production by between 0.33 to 2.69 cents/liter. Although such cost reductions (primarily realized through the sale of the germ) have been helpful, further cost reductions are still necessary for dry-grind ethanol plants to remain competitive.